Edited by: M. Papadrakakis and B.H.V. Topping

Keywords: bitumen, asphalt, pavement, viscoelasticity, cracking, multiscale model, upscaling, identification, validation, FEM, thermal loading.

The increase of heavy-load traffic within Europe requires the development of appropriate tools for the assessment of existing and new road infrastructure. In this paper, such a tool is presented, combining multiscale material modeling of asphalt with structural analysis of flexible pavements at low temperatures. At this temperature regime, rapid cooling of the road surface in consequence of temperature drops may result in so-called top-down cracking. These cracks, when propagating further into the base layer, significantly reduce the service life of road infrastructure. Within the proposed multiscale model for asphalt, the temperature-dependent viscoelastic properties of asphalt are related to the binder material (bitumen), the only material phase exhibiting thermorheological behavior, accounting for

• the large variability of asphalt mixtures, resulting from different mix design, different constituents (e.g., bitumen, filler, aggregate), and the allowance of additives, and
• changing material behavior in consequence of thermal, chemical, and mechanical loading.

In the case of multiscale modeling of the viscoelastic nature of bituminous mixtures, the parameters of the underlying viscoelastic model are obtained from upscaling from the respective parameters identified at the bitumen-scale towards the macroscale. Hereby, the viscoelastic behavior of bitumen serves as input and the effect of the addition of aggregates, i.e., filler, sand, and stone is considered. Upscaling of viscoelastic properties is performed in the framework of continuum micromechanics, employing the Mori-Tanaka scheme [1]. Within the elastic-viscoelastic correspondence principle, the elastic shear compliance in the equations employed for upscaling of elastic properties is replaced by the respective Laplace-Carson transform [2] of the viscoelastic compliance [3]. The so-obtained macroscopic model parameters are employed in the numerical analysis of flexible pavements, giving access to stresses resulting from (i) a sudden drop of the surface temperature in consequence of changing weather conditions and (ii) traffic loading. Comparison of the so-obtained surface stresses with the tensile strength of asphalt at the respective surface temperature allows the assessment of the risk of top-down cracking in flexible pavements.

[1]

T. Mori, K. Tanaka, "Average stress in a matrix and average elastic energy of materials misfitting inclusions", Acta Metallurgica, 21:571-574, 1973.

[2]

J. Mandel, "Méchanique des milieux continues [Mecanics of continuous media]", Gauthier, Paris, 1966. In French.

[3]

E.G. Aigner, R. Lackner, Ch. Pichler, "Micromechanics-Based Determination of Viscoelastic Properties of Asphalt Concrete", Journal of Materials in Civil Engineering (ASCE), 2007. Submitted for publication.

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